The present invention relates to an electrophotographic photoconductor (also referred to hereinafter as xe2x80x9ca photoconductorxe2x80x9d) in particular, the present invention relates to a photoconductor having an improved photosensitive material in a photosensitive layer containing organic materials formed on a conductive substrate. The photoconductor of the present invention exhibits an excellent potential retention rate. Such a photoconductor is used preferably in a printer, a copier or a facsimile machine that employs an electrophotographic process. The present invention also relates to a method for manufacturing such a photoconductor.
Electrophotographic photoconductors are generally required to maintain surface charges in the dark, generate charges upon receipt of light, and transport charges upon receipt of light. The conventional types of photoconductors include a so-called single-layer type photoconductor, having these functions in a single layer, and a so-called function-separated laminated-layer type photoconductor, having a layer that mainly serves to generate charges and a layer that serves to maintain surface charges in the dark and to transport charges upon receipt of light.
These conventional photoconductors are used for forming images by known electrophotographic methods, such as the Carlson method. The image formation of this method is performed by charging the photoconductor by a corona discharge in the dark, forming an electrostatic latent image, such as characters or drawings of an original, on the charged surface of the photoconductor, developing the thus formed electrostatic image by means of toner powder, transferring and fixing the toner powder representing the image onto a support, such as paper. After the toner transfer, the residual toner powder is removed, and residual charges are erased by light exposure, so that the photoconductor can be used again.
As photosensitive material of the electrophotographic photoconductor, practitioners have used inorganic photoconductive substances, such as selenium, selenium alloys, zinc oxide and cadmium oxide, dispersed in a resin binder, as well as organic photoconductive substances, such as poly-N-vinylcarbazole, poly(vinyl anthracene), phthalocyanine compound or bisazo compound, dispersed in a resin binder or subjected to vacuum deposition, for example.
In these organic photosensitive materials, synthesis methods for a phthalocyanine compound have been extensively studied, including the derivative impurities that are side products in the synthesis process. Japanese Unexamined Patent Application Publication (KOKAI) No. H3-35245 discloses studies on the side product of titanyloxo(chlorophthalocyanine) in the synthesis process of titanyloxophthalocyanine. This publication describes that chlorine inclusion of 0.38 to 5 wt % has been confirmed by the examples until that time. The reference further discloses detailed studies on the synthesis process of titanyloxophthalocyanine which process does not generate a by-product of a chlorophthalocyanine.
Further, an example of a molecular structure of a phthalocyanine compound is known, in which an o-phthalonitrile compound is bonded as a ligand, as disclosed by I. M. Keen and B. W. Malerbi, in J. Inorg. Nucl. Chem., vol. 27, p.1311-1319 (1965). The reference discloses, as examples of metal phthalocyanine compounds having a molecular structure in which an o-phthalonitrile compound is bonded as a ligand; (phthalocyanino) chlororuthenium(III) monophthalonitrilate, (phthalocyanino) chloroosmium(III) monophthalonitrilate, (phthalocyanino) dioxoosmium(VI) monophthalonitrilate, and (monochlorophthalocyanino) chloroiridium(III) monophthalonitrilate.
However, this kind of metal phthalocyanine has not been disclosed by any other reference except for the above-cited reference by I. M. Keen et al. In particular, the exemplified metal phthalocyanines in the reference are limited to the elements of the platinum group, and the other metal phthalocyanine compounds having phthalonitrile compound ligand have not been disclosed. Thus, there has never been any study on relationship between content of that kind of metal phthalocyanine and a potential retention rate in a photoconductor.
Japanese Unexamined Patent Application Publication (KOKAI) Nos. H5-273775 and H9-230615 disclose that a titanylphthalocyanine reacts with a diol to form a titanium complex. However, these references aim to obtain a photoconductor of high sensitivity, rather than to achieve high potential retention rate. Furthermore, they do not mention a metal phthalocyanine compound having an o-phthalonitrile compound ligand.
As described above, it is well known to use a phthalocyanine compound for a photosensitive material in a photoconductor. Numerous studies have been made on the synthesis, purification and side products involving the compound. However, electrophotographic photoconductor characteristics have not clarified, until now, with respect to the substances that are the products in polymerization of a phthalonitrile compound and are not likely to contain chlorine. Although studies on various synthesis methods of a phthalocyanine compound have been disclosed, the relation of the types and contents of the side products accompanied by synthesis of a phthalocyanine compound to the electrophotographic characteristics, especially, to the potential retention rate has not been clarified. A relationship between content and potential retention rate with respect to the metal phthalocyanine being bonded by a phthalonitrile compound as a ligand, in particular, has never yet been studied.
It is an object of the present invention to provide an electrophotographic photoconductor which overcomes the foregoing problems.
It is a further object of the present invention to provide an electrophotographic photoconductor that exhibits an excellent electrophotographic characteristic, specifically, an excellent potential retention rate.
It is another object of the invention to provide a method for manufacturing an electrophotographic photoconductor including a step for forming a photosensitive layer by coating a coating liquid, the step allowing to form a photosensitive layer of an excellent potential retention rate.
Briefly stated, the present invention provides a photosensitive layer of an electrophotographic photoconductor having at least one phthalocyanine compound, wherein the photosensitive layer contains a metal phthalocyanine compound bonded by an o-phthalonitrile compound as a ligand. The o-phthalonitrile ligand is present in an amount from about 100 nmol to about 200 nmol with respect to 1 mol of the phthalocyanine. The resulting electrophotographic photoconductor exhibits a high potential retention rate. A method for making such an electrophotographic photoconductor is also disclosed wherein a photosensitive layer is formed by coating, with a coating layer, to obtain a photosensitive layer having a high potential retention rate.
According to an embodiment of the present invention, there is provided a An electrophotographic photoconductor, comprising a conductive substrate, a photosensitive layer on the conductive substrate, the photosensitive layer containing at least one phthalocyanine compound as a photosensitive material on the conductive substrate, and the photosensitive layer contains a metal phthalocyanine compound bonded by an o-phthalonitrile compound as a ligand, in an amount of from about 100 nmol to about 200 mmol with respect to 1 mol of said phthalocyanine compound.
According to a feature of the present invention, there is provided a method for manufacturing an electrophotographic photoconductor, comprising providing a conductive substrate, and forming a photosensitive layer by coating the conductive substrate with a coating liquid containing at least one charge generating substance, wherein the coating liquid contains a phthalocyanine compound and a metal phthalocyanine compound bonded by an o-phthalonitrile compound as a ligand, and the metal phthalocyanine compound is contained in an amount from about 100 nmol to about 200 mmol with respect to 1 mol of the phthalocyanine compound.
The inventors of the present invention have made numerous studies to solve the foregoing problems and found that the retention rate of a photoconductor substantially increases when a metal phthalocyanine compound bonded by an o-phthalonitrile compound as a ligand (also referred to hereinafter as xe2x80x9ca ligand-bonded metal phthalocyaninexe2x80x9d) is contained in the layer including a phthalocyanine compound of the photosensitive layer in a specified range of content: The present invention has been accomplished according to the finding.
Thus, an electrophotographic photoconductor according to the present invention comprises a conductive substrate and a photosensitive layer thereon containing a phthalocyanine compound as a photosensitive material, wherein the photosensitive layer containing the phthalocyanine compound includes a metal phthalocyanine compound bonded by an o-phthalonitrile compound as a ligand in an amount of from about 100 nmol to about 200 mmol with respect to 1 mol of the phthalocyanine compound.
Moreover, the inventors of the present invention found that, a potential retention rate of a photoconductor substantially increases when such a coating liquid containing a charge generating substance is used in a coating step in a method for manufacturing the photoconductor that includes a phthalocyanine compound and a ligand-bonded metal phthalocyanine compound, the content of the latter with respect to the former being in a specified range. The finding lead to accomplishment of the manufacturing method of the invention.
Thus, a method for manufacturing a photoconductor according to the present invention comprises a step for forming a photosensitive layer by coating a conductive substrate with a coating liquid containing a charge generating substance, wherein the coating liquid includes a phthalocyanine compound and a metal phthalocyanine compound bonded by an o-phthalonitrile compound as a ligand, the content of the metal phthalocyanine being from about 100 nmol to about 200 mmol with respect to 1 mol of the phthalocyanine compound.
The photosensitive layer in the photoconductor of the invention may be either a single-layer type or a laminated-layer type, and is not limited to any one of the two types. The coating method in the manufacturing method of the invention may be selected from dip coating, spray coating, and other various method, and is not limited to any specific method.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.